• 14C Analyses of Groundwater from the Botucatu Aquifer System in Brazil

      Silva, Annkarin Aurelia Kimmelmann E.; da Cunha Rebouças, Aldo; Freitas Santiago, Maria Marlucia (Department of Geosciences, The University of Arizona, 1989-01-01)
      Measurements of 14C activity as well as determinations of the stable isotope composition (18O, 2H and 13C) of groundwater samples were made to investigate the flow path, origin, recharge and age of the Botucatu Aquifer System in Brazil, between 1984 and 1987. The stable oxygen isotope composition reflects infiltration during several climatic recharge conditions. Measured 14C activities range from 0.4 to 94.2% modern. delta-13C values enable us to distinguish two groundwater types of different origins. There is a gradual increase of 14C ages from the outcrop area towards the central part of the basin, associated with a progression of the confining conditions. Anomalous fluoride contents seem to be correlated with high 14C ages of the groundwater. The reliability of the 14C data is discussed.
    • 14C Dating with the Gif-sur-Yvette Tandetron Accelerator: Status Report and Study of Isotopic Fractionation in the Sputter Ion Source

      Arnold, Maurice; Bard, Edouard; Maurice, Pierre; Valladas, Helene; Duplessy, J. C. (Department of Geosciences, The University of Arizona, 1989-01-01)
      The standard procedure for measuring 14C at the Gif-sur-Yvette Tandetron AMS facility is described. A new sample manipulator and automated measurements are being used and have been operational for six months. Evidence of isotopic fractionation in the sputter ion source is provided. We take this into account by measuring the 13C/12C ratio of the sample in the accelerator.
    • 14C in the Environment of Swiss Nuclear Installations

      Loosli, Heinz Hugo; Oeschger, Hans (Department of Geosciences, The University of Arizona, 1989-01-01)
      The results of a 10-year survey of 14C content in tree leaves from the vicinity of Swiss nuclear installations are reported. The interpretation is based on the results from a reference station showing a systematic decrease from Delta-14C = +350 per mil in 1977 to ca +190 per mil in 1987. Excess activities of up to ca 100 per mil are observed in the vicinity of nuclear power plants which are compatible with release rates and dilution calculations. A higher excess of up to 1400 per mil is measured in the close vicinity of a small research plant which releases the activity on top of the roof. The determined decrease of the activity with distance can be described by a power law with ca -1.4 in the exponent. Additional doses of 14C to plants and population from excess 14C activities are estimated to be negligible compared to natural doses.
    • 14C Profiles in the Central Weddell Sea

      Schlosser, Peter; Kromer, Bernd; Bayer, Reinhold; Münnich, K. O. (Department of Geosciences, The University of Arizona, 1989-01-01)
      14C data from stations in the central Weddell Sea are presented and discussed using additional parameters (potential temperature, salinity and 3He). The low 14C concentrations of the surface water (approximately equal -90 per mil) are explained by suppressed gas exchange due to ice cover during the winter and rapid turnover of the surface layer caused by entrainment of Warm Deep Water (WDW) with low 14C concentrations. A simple time-dependent balance calculated for the Surface Water (SW) and the underlying Winter Water (WW) can reproduce the 14C concentrations observed in these layers for 1985. The pre-bomb 14C concentrations are estimated at approximately equal to -130 per mil for SW and -140 per mil for WW. A strong deviation of the SW 14C concentration observed in 1973 from the calculated value suggest a change in surface circulation and/or air/sea exchange during the period before the Weddell Polynya in 1974. The observed 14C concentrations of the Weddell Sea Bottom Water (WSBW; -135 to -150 per mil) are only slightly higher than those of the WDW showing that the uptake of bomb 14C in the Weddell Sea is limited. The 14C profiles show a minimum at intermediate depths (approximately equal to 1500m) which is caused by radioactive decay and/or penetration of bomb 14C from shallow and deep layers (WDW and WSBW) into intermediate layers.
    • 14C Release in Various Chemical Forms with Gaseous Effluents from the Paks Nuclear Power Plant

      Hertelendi, Ede; Uchrin, György; Ormai, Peter (Department of Geosciences, The University of Arizona, 1989-01-01)
      We present results of airborne 14C emission measurements from the Paks PWR nuclear power plant. Long-term release of 14C in the form of carbon dioxide or carbon monoxide and hydrocarbons were simultaneously measured. The results of internal gas-proportional and liquid scintillation counting agree well with theoretical assessments of 14C releases from pressurized water reactors. The mean value of the 14C concentration in discharged air is 130Bgm 3 and the normalized release is equal to 740GBq/GWe yr. > 95% of 14C released is in the form of hydrocarbons, ca 4% is apportioned to CO2, and <1% to CO. Tree-ring measurements were also made and indicated a minute increase of 14C content in the vicinity of the nuclear power plant.
    • 14C Tephrochronology with Different Fractions of Paleosol Humic Matter at Procida Island, Italy

      Alessio, Marisa; Allegri, Lucia; Azzi, Carlo; Calderoni, Gilberto; Cortesi, Cesarina; Improta, Salvatore; Petrone, Vincenzo (Department of Geosciences, The University of Arizona, 1989-01-01)
      14C apparent ages along with delta-13C values for three different fractions of humic matter (HM) isolated from a suite of four paleosols (PAs) interbedded within tephra are reported. The dated HM fractions were: 1) HA, the easily released humic acids; 2) HAtot, the bulk of humic acids; 3) RES, the insoluble HM. The 14C sequence dated from 13,000-25,000 BP, in agreement with stratigraphy and previous data. Age differences up to 2540 +/- 430 were statistically significant among fractions; their order of magnitude being independent from C content and depth. All the PAs showed a common pattern of among-fraction age variation, 14C agingltrending from RES to HA101 through HA. As the HM fractions exhibited quite comparable delta-13C values (delta-13C = -25.4 +/- 0.2 per mil), it is inferred that the primitive organic matter (OM) input to PAs was dominantly supplied by vegetation of C-3 photosynthetic pathway which underwent complete decomposition during diagenesis.
    • 14CARE

      Polach, Henry (Department of Geosciences, The University of Arizona, 1989-01-01)
      The need for and means of achieving a 14C dating quality assurance service are debated.
    • 41Ca Concentrations in Modern Bone and Their Implications for Dating

      Middleton, Roy; Fink, David; Klein, Jeffrey; Sharma, Pankaj (Department of Geosciences, The University of Arizona, 1989-01-01)
      We have made the first measurements without pre-enrichment of 41Ca in terrestrial rock and bone samples using accelerator mass spectrometry. Although the results in tufa deposits from Egypt are in good agreement with the saturation value of 8 x 10^-15 predicted by Raisbeck and Yiou (1979), the average 41Ca:40Ca ratio of 2x10^-15 (range: 0.6 to 4.2x10^-15) that we measure in modern bone is an order of magnitude lower than that obtained previously by Henning, et al (1987) on a cow bone that was measured using AMS following isotope enrichment. The low value and the variability (more than a factor of seven) of the 4 Ca:40Ca ratio in modern bone make the possibility of dating bones using 41Ca unlikely.
    • A 36Cl Profile in Greenland Ice from AD 1265 to 1865

      Conard, N. J.; Gove, H. E.; Elmore, David (Department of Geosciences, The University of Arizona, 1989-01-01)
      We have measured the concentration of 36Cl in 67 samples from the upper portion of the Camp Century ice core. The profile extends from AD 1265 to 1865 and covers the times of the Wolf (AD 1282-1342), Spoerer (AD 1416-1534) and Maunder (AD 1645-1715) minima in sunspot number. Although the profile exhibits much short-term variation, a smoothed plot of the data shows a strong peak in 36Cl concentration over the time of the Maunder Minimum. The deeper part of the core suggests increased deposition of 36Cl over the periods of the Wolf and Spoerer minima. The time resolution of the profile is inadequate for testing for an 11-year periodicity in our data. The data augment evidence from 10Be and 14C studies which indicate solar modulation of radioisotope production. Since, however, much of the short-term variation of 36Cl seems to be independent of solar activity, other factors must affect the deposition of 36Cl in ice. These variations could be due in part to mechanisms affecting the transport of 36Cl in the atmosphere. Based on our data from Camp Century, we calculate an average input of 36Cl of 24 atoms/m2 sec.
    • A Beta Test Comparison Between the New Packard 2260 XL and the LKB Quantulus and 1219 SM: Low-Level Radiocarbon and Tritium Determinations

      Kalin, Robert M. (Department of Geosciences, The University of Arizona, 1989-01-01)
      A Packard 2260 XL liquid scintillation counter was placed in an underground counting chamber to test performance under immense physical shielding. Results from the Packard 2260 XL are compared with two other counters under the same conditions, the LKB Quantulus, which has operated for two years in this laboratory, and the LKB 1219 SM, in use since January 1988.
    • A Comparison of Methods Used for the Calibration of Radiocarbon Dates

      Aitchison, T. C.; Leese, Morven; Michczynska, Danuta J.; Mook, W. G.; Otlet, R. L.; Ottaway, B. S.; Pazdur, Mieczysław F.; van der Plicht, Johannes; Reimer, P. J.; Robinson, S. W.; et al. (Department of Geosciences, The University of Arizona, 1989-01-01)
      Current calibration methods for single and replicate 14C dates are compared. Various forms of tabular and graphic output are discussed. Results from all the methods show reasonable agreement but further methodological development and improvements in computer output are required. Comparison of existing techniques for a series of non-contemporaneous dates showed less agreement amongst participants on this issue. We recommend that calibrated dates should be presented as a combination of graphs and ranges, in preference to mean and standard deviation.
    • A Counter System for High-Precision 14C Dating

      Hertelendi, Ede; Csongor, Éva; Zaborszky, Laszlo; Molnar, Jozef; Gal, Janos; Györffi, Miklos; Nagy, Sandor (Department of Geosciences, The University of Arizona, 1989-01-01)
      A multicounter radiocarbon dating system was developed applying the experiences of the previous one-channel low-level counting facility. The counter system consists of nine electrolytic copper proportional counters of identical diameters with sensitive volumes of 0.35-0.7dm3 and filled with either methane at high pressure (6 bar) or CO2 at 1 bar. The inner counters are surrounded by an anticoincidence shield consisting of five multiwire proportional flat counters filled with propane. The pulses of the detectors are handled by integrated amplifiers, discriminators and anticoincidence units interfaced to a microprocessor-controlled data evaluation unit. Software is written in BASIC using ASSEMBLER sub-routines. The overall precision of the system for modern carbon samples using high-pressure methane-filled counters (B is approximately equal to 0.7 cpm, S is approximately equal to 14 cpm) is better than 4 per mil after a counting period of seven days.
    • A Critical Review of Radiocarbon Dating of a Norse Settlement at L'Anse Aux Meadows, Newfoundland, Canada

      Nydal, Reidar (Department of Geosciences, The University of Arizona, 1989-01-01)
      Recent progress in high-precision calibrations of radiocarbon dates has led to evaluations of earlier research. This has been the case with dates from the Norse settlement at L'Anse aux Meadows which was discovered by Helge Ingstad in 1960. The most problematic feature of this series up to now was the use of sample material which partly derived from driftwood. The present paper concludes that charcoalfrom this site demonstrated no greater errors than normal from other settlement sites. With an assumed total systematic error of 30 +/- 20 years, as a mean for various tree rings, the calibrated age range of L'Anse aux Meadows is AD 975 -1020. This agrees well with the assumed historical age of ca AD 1000, a result which has also been recently corroborated by high-precision accelerator dating at the University of Toronto.
    • A Cyclogram Analysis of the Bratislava 14C Tree-Ring Record During the Last Century

      Attolini, M. R.; Galli, Menotti; Nanni, Teresa; Povinec, Pavel (Department of Geosciences, The University of Arizona, 1989-01-01)
      Radiocarbon variations in dated tree-ring samples represent an important tool for the study of the history of solar activity and sun-earth relationships. From this point of view, an investigation of the 11-year radiocarbon cycle is very important. Our cyclogram analysis of the Delta-14C record in tree-ring samples during the last century has confirmed previous results obtained by conventional harmonic analysis, eg, the average amplitude of 2%, the phase shift of 3-5 yr for different 11-yr solar cycles, and the anticorrelation dependence of Delta-14C on Wolf sunspot numbers. The observed shorter periodicity (ca 9 yr for Delta-14C compared to 10.5 yr for sunspots), may be due to extra factors in sun-earth relationships.
    • A Semi-Automated Bone Pretreatment System and the Pretreatment of Older and Contaminated Samples

      Law, I. A.; Hedges, R. M. (Department of Geosciences, The University of Arizona, 1989-01-01)
      A semi-automated continuous-flow system used to process archaeological bone to purified gelatin or amino acids for 14C dating is described. Powdered bone is retained in flow cells specifically designed to permit the sequential leaching of the bone with acid, alkali and water. Crude collagen obtained by this process is gelatinized, and than either purified directly using a macroporous cation exchange resin (BioRad AGMP-50), or hydrolyzed and the amino acids desalted on BioRad 50W-X8 resin. When compared with previous methods used by the laboratory, the new method allows more samples to be treated to a higher degree of purification. Examples of dates obtained on "standard" bones are presented, and confirm that no contamination is introduced from the components used in the new process.
    • Accelerator-Measured 14C Activity in Tree Rings from the Vicinity of the First Atomic Bomb Test

      Leavitt, S. W.; Long, Austin (Department of Geosciences, The University of Arizona, 1989-01-01)
      Detonation of the first fission bomb at White Sands, New Mexico, on July 16, 1945, produced a tremendous neutron flux capable of creating tritium and radiocarbon byproducts. We sampled a 115-year-old pinyon (Pinus edulis) 10km east of the Trinity test site to determine 14C evidence of this event. The most likely mechanism for this enrichment in the 1945 tree ring would be fixation of 14CO2 produced at the blast site and carried with the fallout cloud over the pinyon site. Analysis of cellulose of the 1944 and 1945 rings shows delta-13C values of -19.9 and -19.5 per mil, respectively, and 14C activity (fraction of modern uncorrected for delta-13C) as 0.991 +/- .005 and 0.991 +/- .006, respectively. It is likely that the duration and/or concentration of the 14CO2 exposure was not sufficient to increase 14C activity expected for that year.
    • Account of the Business Meeting at Dubrovnik, 24/6/88

      Mook, Willem G. (Department of Geosciences, The University of Arizona, 1989-01-01)
    • AMS 14C Dating on the Fossvogur Sediments, Iceland

      Andersen, G. J.; Heinemeier, Jan; Nielsen, H. L.; Rud, Niels; Thomsen, M. S.; Johnsen, Sigfús; Sveinbjörnsdóttir, Árný E.; Hjartarson, Árni (Department of Geosciences, The University of Arizona, 1989-01-01)
      Several new AMS 14C dates on shells from the Fossvogur sea sediments in southern Iceland are reported. Up till now, researchers have assumed that the Fossvogur sediments formed during the last interglacial period (Eem), some 100,000 years ago. However, a recent 14C determination from this location yielded an age of ca 11,000 yr. Because of the importance of these sediments for the Quaternary chronology of Iceland, further sampling for 14C dating was subsequently initiated. The present results on several shell samples collected from the Fossvogur layers strongly indicate that these sediments were formed during the warm Allerød period toward the end of the last glaciation.
    • AMS 14C Measurements of Fractionated Soil Organic Matter: An Approach to Deciphering the Soil Carbon Cycle

      Trumbore, Susan E.; Vogel, J. S.; Southon, J. R. (Department of Geosciences, The University of Arizona, 1989-01-01)
      14C measurements are reported for fractionated soil organic matter from a genetic soil sequence which was sampled several times during the period of atmospheric nuclear weapons testing. Fractionation of the soils by density followed by acid hydrolysis was successful in separating the organic matter into components with mean residence times for carbon ranging from 5 to 20 years (low density fraction) to several thousand years (residue after acid hydrolysis). Comparison of the infiltration of bomb 14C into the vertical soil profile with the distribution of 137Cs, gives clues as to the mechanism (most probably dissolved transport) for importing carbon into deeper soil layers.
    • AMS 14C Study of Transient Events and of the Ventilation Rate of the Pacific Intermediate Water During the Last Deglaciation

      Duplessy, Jean-Claude; Arnold, Maurice; Bard, Edouard; Juillet-Leclerc, Anne; Kallel, Nejib; Labeyrie, Laurent (Department of Geosciences, The University of Arizona, 1989-01-01)
      14C analysis of monospecific samples of planktonic and benthic foraminifera were performed in deep-sea sediment cores from the Atlantic and Pacific Oceans by Accelerator Mass Spectrometry (AMS). These measurements demonstrate that the Younger Dryas cold event, first described in the north Atlantic, is also present at the same time in the north Pacific Ocean. The comparison of the 14C ages of planktonic and benthic foraminifera from the same sediment level in two Pacific cores shows that the ventilation time of the Pacific Ocean was greater than today during the last ice age, but significantly less than today during the deglaciation.